Cross-bar matrix for connecting digital resources to I/O pins of an integrated circuit

ABSTRACT

A matrix of routing cells forming a cross-bar decoder ( 310 ). Signal triplets are coupled through the cross-bar decoder ( 310 ) based on control by a microprocessor. A register ( 50 ) provide control signals to the cross-bar decoder ( 310 ) to either activate or deactivate routing of the triplet signals through cells of the cross-bar decoder ( 310 ). The routing cells are arranged in a matrix of columns and rows. Each row of cells is associated with a common data signal input, and each column of the matrix is associated with a common I/O pin. The cells are individually enabled by the microprocessor so that any data signal can be coupled to any of the I/O pins. In addition to routing data signals through the cells, other signals are also routed through the cells.

RELATED APPLICATION

This application is Continuation of application Ser. No. 09/583,260,filed on May 31, 2000, entitled CROSS-BAR MATRIX FOR CONNECTING DIGITALRESOURCES TO I/O PINS OF AN INTEGRATED CIRCUIT, which will issue as U.S.Pat. No. 6,738,858, on May 18, 2004, and is related to U.S. applicationSer. No. 09/584,308, entitled PRIORITY CROSS-BAR DECODER.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to integrated circuitinput/output circuits, and more particularly to a matrix arrangement forproviding switched access of a plurality of signals to I/O ports.

BACKGROUND OF THE INVENTION

The large scale integration of a number of devices or circuits allowsnumerous functions to be carried out within a single integrated circuit.On the one hand, semiconductor dies or chips can be made larger toaccommodate a larger number of circuits and corresponding functions.Conversely, significant improvements in lithography techniques have beenachieved in order to make the existing circuits smaller so thatadditional circuits can be formed within a chip, without utilizing alarger-sized semiconductor chip. In order to utilize the functionsprovided by the circuits formed within the chip, I/O pins or ports arenecessary. In some situations, if additional I/O pins are needed, thenthey are simply added to the chip as a metallic pad or pin. It can beappreciated that, based on a given size of the semiconductor die, only areasonable number of I/O pins can be accommodated. Some integratedcircuits, especially those that are microprocessor-based, have more thanone hundred I/O pins. The I/O pins can be formed not only on the edge ofthe chip, but also on the planer face of the chip.

A problem exists when there are more signals or functions thancorresponding pins available to the integrated circuit. One practice hasbeen to multiplex a few number of signals, such as two or three, withrespect to a single I/O pin. The multiplexing is carried out by a simplelogic circuit that selects one of the three signals to use the I/O pinat any given time. Although this limited I/O pin sharing featureprovides a certain degree of flexibility, there exists other situationsin which this solution is not acceptable. There are various applicationsin which an integrated circuit provides more functions than can beaccommodated by a full pin-out integrated circuit. In such situations,it is often the case that not all functions are required at the sametime. In other applications, different users require the standardintegrated circuit to be packaged with fewer than the standard number ofI/O pins. In both applications, the dilemma is not easily overcome.

From the foregoing, it can be seen that a need exists for a technique toimprove the flexibility by which the various signals or functions of anintegrated circuit device are made available to the I/O pins. Anotherneed exists for a switch matrix that allows many different signals orfunctions to be applied to many different I/O pins, while yet minimizingthe semiconductor area utilized.

SUMMARY OF THE INVENTION

In accordance with the principles and concepts of the invention, thereis disclosed a switching matrix that allows a plurality of differentsignals to be applied to each of a fewer number of I/O pins of a device.In accordance with a preferred form of the invention, a logic cell isreplicated to form a cross-bar switching matrix so that the varioussignals generated on a chip can be routed to desired I/O pins. Thesignals can thus be routed to the I/O pins based on assignment by amicroprocessor.

The cross-bar matrix includes plural cells defining rows and columns.Each row of cells receives a common data signal from a data resources,and each column of cells is associated with a common I/O pin of theintegrated circuit. Each cell of a row receives a separate enable orcontrol signal which enables a cell to couple therethrough the datasignal to the corresponding I/O pin. In the preferred form, only onecell in a row is enabled for that row. The microprocessor controls whichcell of each row is to be enabled so that the various signals arecoupled to the desired I/O pins. By utilizing a cross-bar matrix, anydata signal can be coupled to any of the I/O pins.

In addition to coupling data signals through the cells of the matrix, anoutput enable signal is also coupled from the data resource to thedesired driver circuit of the I/O pin. Each cell includes a logiccircuit controlled by the enable signal to allow coupling through thecell to the I/O driver circuit the output enable signal. The outputenable signal controls the I/O driver circuit so that the I/O pin beconfigured either as an input pin or as an output pin, or both.

The designs of each matrix cell is made such that bidirectional signalscan be coupled therethrough. To that end, each cell includes a logiccircuit responsive to the enable signal for that cell, for coupling datasignals input from the I/O pin to the data resource.

A high degree of flexibility is thus available in coupling the differentsignals between the data resource and the I/0 pins of the integratedcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will be apparent from the following andmore particular description of the preferred and other embodiments ofthe invention, as illustrated in the accompanying drawings in which likereference characters generally refer to the same parts or elementsthroughout the views, and in which:

FIG. 1 illustrates a generalized block diagram of the priority cross-bardecoder and support circuits according to the preferred embodiment ofthe invention;

FIG. 2 illustrates a diagram of a priority assignment of various signalsto the various I/O pins of the integrated circuit;

FIG. 3 illustrates a detailed schematic drawing of a priority cross-bardecoder, in which three different signals can be assigned and routed tothree different I/O pins;

FIG. 4 illustrates a simplified diagram of the various cells of thecross-bar decoder of FIG. 3;

FIG. 5 illustrates the I/O pin driver circuits coupled to the prioritycross-bar decoder;

FIG. 6 illustrates the priority cross-bar decoder of FIG. 3, but withoutone cell of the matrix;

FIG. 7 illustrates a simplified diagram of the cross-bar decoder of FIG.6;

FIG. 8 illustrates a four-by-five matrix of cross-bar decoder cells,with various circuits shown in enlarged form; and

FIG. 9 illustrates a matrix of routing cells for routing data resourcesignals to I/O pins, without the use of priority.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the various digital resources and other supportcircuits of a semiconductor chip that can be employed and otherwisecontrolled by a microprocessor (not shown) on the same chip. The aim ofany processor system is to couple the digital resources, as well as theI/O ports of the processor itself, to the terminal pins associated withthe semiconductor chip. As noted above, most pins of microprocessorchips are assigned one or two functions, but are limited to suchfunctions. This represents a major shortcoming, especially if thesemiconductor chip is small in area, thereby leaving very little roomfor I/O pins.

In FIG. 1, there is shown a priority cross-bar decoder 10 for couplingthe digital resources 12 to the various I/O pins 14 of the chip. Thepriority of each I/O pin is shown. The various digital resources 12,from the highest to lowest priority, include two bits of a systemmanagement bus 20, four bits of a serial peripheral interface 22, twobits of a UART 24, six bits of a programmable counter array 26, two bitsfor a pair of comparators 27, and six bits for various timers 28. Alsoinput to the priority cross-bar decoder 10 is a system clock (SYSCLK)30. Output from the cross-bar decoder 10 is a conversion start (CNVSTR)signal 32. The priority of the signals of the digital resources isshown. Three 8-bit buses 34-36 are also provided as microprocessor portinputs and outputs to the priority cross-bar decoder 10. A fourthmicroprocessor bus 38 bypasses the priority cross-bar decoder 10 and iscoupled directly to respective eight I/O pins 40 via I/O pin drivercircuits 42. The I/O driver circuits 42 are controlled by respectiveregisters 44 in a manner to be described below.

The priority cross-bar decoder 10 includes a number of replicated cells48 for coupling digital signals from the digital resources 12, based onpriority, to the respective I/O pins 14. The priority function of thecross-bar decoder 10 is integrated on the microprocessor chip with logicgates. A number of cross-bar registers (XBR) 50 are written or otherwisecontrolled by the microprocessor. When the cross-bar registers 50 arewritten by the microprocessor, the various signals from the digitalresources 12 are activated and are passed through the cross-bar decoder10 to the assigned I/O pins 14. Generally, but not exclusively, a singleoutput of the XBR register 50 is effective to select a group of signalsof digital resource 12. In the preferred form of the invention, onecross-bar register output will select the two signals of the digitalresource 20, a second cross-bar register output will select the foursignals of the digital resource 22, and so on. Other digital resources,such as resource 28, may have each signal thereof selected by a separatecross-bar register output. In practice, there are three 8-bit cross-barregisters, designated XBR0, XBR1 and XBR2. If the first bit of the XBR0register is enabled and set to a logic one, then both signalscorresponding to the SMbus resource 20 are enabled to be routed throughthe priority cross-bar decoder 10. As can be seen, the particularapplication involved will dictate the correspondence between the typeand number of digital resource signals selected by cross-bar registeroutputs.

Since the SMbus 20 is assigned the highest priority, the two signalsthereof will be automatically routed to highest priority pins, namelypins 0 and 1 of I/O port 0. The I/O pins 14 illustrate three 8-bitports. The digit to the left of the decimal point illustrates the portnumber, and the digit to the right of the decimal point illustrates thepin number of that port. The first signal of the SMbus 20 would berouted by the priority cross-bar decoder 10 to port 0, pin 0 (P0.0), andthe second signal of the SMbus 20 would be coupled to port 0, pin 1(P0.1). In practice, if the SMbus 20 was not utilized, then the firsttwo signals of the serial peripheral interface 22 would be coupledrespectively to port 0, pins 1 and 2 and the second two signals of theserial peripheral interface 22 would be coupled to port 0, pins 2 and 3.Hence, the lower order port and pins are assigned and utilized for thebidirectional transfer of signals, and any unassigned I/O pins are thelower priority I/O pins. The most unused pin in this scheme is the lastor lowest priority pin, namely port 2, pin 7. The existence of anyunassigned I/O pin assumes that fewer than twenty-four signals areactivated.

It should be noted that the priority cross-bar decoder 10 contains anumber of routing circuits or cells 48, each of which has a path thatcan route digital signals in one direction, and a separate path forpassing digital signals in the opposite direction. These two signalpaths provide a bidirectional transfer capability to and from the I/Opins 14. In addition, a third path is routed through each cell 48 of thepriority cross-bar decoder 10 to provide an enable signal. The state ofthe enable signal determines whether the I/O pin is configured as aninput or an output. Thus, for example, the SMbus digital resource 20 isshown to have two signal buses. Indeed, each signal bus constitutesthree separate conductors that are routed through the priority cross-bardecoder 10. This will be described in more detail below.

Coupled between the priority cross-bar decoder 10 and the I/O pins 14are respective I/O drive circuits 52. The I/O drive circuits 52 can beconfigured by a number of port registers 54. In the preferred form ofthe invention, since there are three I/O ports, each with 8 pinsassociated therewith, there are a corresponding three 8-bit registers,designated PRT0CF, PRT1CF and PRT2CF. The drive circuits 52 can beconfigured to provide the pins with push-pull capabilities, weakpull-up, or high impedance.

With reference to FIG. 2, there is illustrated the priority assignmentof the various digital resource signals, as a function of the I/O portpins. Each port pin is shown at the top of the chart of FIG. 2, whereaseach digital resource signal is shown in a column at the left of thechart. Each dot, for example dot 48, represents the existence of across-bar cell. A blank space, for example space 56, illustrates theabsence of a cell. As noted above, the two SMbus 20 signals are assignedthe highest priority. In particular, the SDA and SCL signals of the SMbus are given the highest priority, and are assigned respectively toport 0, pins 0 and 1. These two signals always activated together, ornot at all, and thus they are assigned different I/O pins. The serialperipheral interface 22 includes four signals, ranked from the highestpriority, and identified as SCK, MISO, MOSI and NSS. The SCK signal isassigned port 0, pin 0, if the SDA signal is not used. If the SDA signalis being used, then the SCK signal is assigned port 0, pin 2. As can beseen by the vacant cell 58, the SCK signal can never be assigned to portP0.1. The vacant cells in the chart corresponding to the various signalsof digital resources 20, 22, 24 and 26 reduce the number of cellsinvolved, and thus allow the priority cross-bar decoder 10 to befabricated in a smaller area of semiconductor material.

While a full 24×24 switching matrix of cross-bar cells could beutilized, it has been found that in many applications this is notnecessary. Various schemes can be utilized to reduce the number ofcross-bar cells in a switching matrix without substantially compromisingthe flexibility or efficiency. With fewer cells, less semiconductor areais required for the switching matrix. By prioritizing the signalsapplied to the switching matrix, fewer cells are required. Indeed, thetriangular shaped area 60 shown in FIG. 2 is not populated withcross-bar cells, and thus the area required for the matrix is much lessthan otherwise might be required. Secondly, by enabling pairs or groupsof signals from the digital resource, a further reduction in the numberof cells is required. Because the two signals (SDA and SCL) of thedigital resource 20 are selected as a pair, they can never be bothassigned and routed to the same I/O pin. As a result, when the SDLsignal is assigned to P(0.0), SCL cannot be assigned to the pin, andthus the cell location 61 for the SCL signal is vacant. The vacant celllocations reduce the area required for implementation of the cross-bardecoder 10.

As the signals associated with the chart of FIG. 2 are assigned lowerpriority, i.e., appear lower in the chart, they have the option of beingconnectable to a greater number of I/O pins. For example, the signalCNVSTR 32 is coupled to a cross-bar cell located in each column thereof,thereby being able to be routed to each one of the 24 I/0 pins. In otherwords, if the first 23 pins are assigned to signals, the CNVSTR signal32 can be assigned to pin P2.7, the last and 24th I/O pin.

Referring now to FIG. 3, there is illustrated a three-by-three prioritycross-bar decoder 70, meaning that three signals are prioritized and canbe coupled to three different I/O pins. FIG. 5, when coupled to FIG. 3,illustrates the connections between the cross-bar decoder 70 and the I/Opin driver circuits. The I/O drivers can be configured to providedifferent functions, as described below. FIG. 4 shows, in simplifiedform, the priority assignment of the various signals with regard to theI/O pins. The first data resource signal is assigned the highestpriority with regard to cell 72, in that it can be connected onlythrough the cross-bar decoder 10 to I/O pin 0. Since the highestpriority signal can always be connected to I/O Pin, it is unnecessary toprovide optional connections to other I/O pins. As noted above, eachsignal applied to the cross-bar decoder 70 includes three conductorsidentified by Sig_(in), Sig_(out) and Enable_(out). Hence, the cross-bardecoder cell 70 carries three switched conductors, each associated withthe three respective signals. Sig0 _(in), Sig0 _(out), and Enable0_(out) are associated with cell 72. Sig1 _(in), Sig1 _(out) and Enable1_(out), are associated with cross-bar decoder cells 74 and 78, and thuscan be coupled to either I/O pin0 or pin 1. Lastly, Sig2 _(in), Sig2_(out), and Enable2 _(out), are associated with cross-bar decoder cells76, 80 and 82 and thus can be switched to any of the three I/O pins. Ifall three digital resource signals are activated by selection of thecross-bar register 50, then the triplet Signal₀ 84 would be assigned toPin0, triplet Signal₁ 86 would be coupled through cell 78 to Pin1, andtriplet Signal₂ 88 would be coupled through cell 82 to Pin 2. Again, iftriplet Signal₀ 84 was not activated by way of the cross-bar register50, then triplet Signal₁ 86 would be coupled to Pin 0 via cell 74. Inlike manner, triplet Signal₂ 88 would be coupled to Pin 1 by way of cell80.

The detailed operation of FIG. 3 is next described. It should berealized that the cross-bar register 50 only selects the various digitalresource signals, but does not assign any priority to the signals.Rather, the priority cross-bar decoder 70 itself assigns a priority tothe signals. The priority assignment of signals to I/O pins can berearranged should one or more of the digital resource signals bedeactivated. The priority is assigned in a ripple-like manner, in thatthe highest priority I/O pins are first utilized for the transfer of thehighest priority signals. Once the highest priority signal that isactivated is assigned to I/O Pin 0, then the cross-bar decoder 70assigns the next highest priority signal that is activated to Pin 1, andso on such that the highest to lowest priority activated signals ripplethrough the cross-bar decoder 70. If one or more of the digital resourcesignals are not activated, the lowest priority I/O pins will be unused.

As noted above, cross-bar decoder cell 72 in the first row is associatedwith triplet signal lines 84. Cross-bar decoder cells 74 and 78 in thesecond row are associated with triplet signal lines 86. Lastly,cross-bar decoder cells 76, 80 and 82 in the third row are associatedwith triplet signal lines 88. Each of the triplets of lines includes asignal-in line, a signal-out line and an enable-out line. Generally, thesignal-in line functions to transfer signals from an assigned I/O pin tothe digital resource 12. The signal-out line is effective to transfersignals from the digital resource 12 to an assigned I/O pin. Theenable-out signal is effective to configure the respective I/O pindriver circuit so that data can be either transmitted from or receivedby the associated pin.

Each priority cross-bar decoder cell in a horizontal row is associatedwith the respective triplet of signal lines. Each triplet of signallines is selected by an output of the cross-bar register 50, three ofwhich are shown by reference numerals 96, 98 and 100 in FIG. 3. Thefirst cross-bar register signal XBR₀ 96 selects the first signal triplet84. The second cross-bar register signal XBR₁ 98 selects the secondsignal triplet 86. The third cross-bar register signal XBR₂ 100 selectsthe third signal triplet 88. In other words, if the first triplet 84 ofsignals is to be selected so that Sig0 _(out) is transferred to I/O Pin0.0, then the XBR₀ signal 96 is driven high by the XBR register. Theoutputs of the XBR registers 50 are set or reset by the microprocessor.Of course, the preferred form of the invention involves twenty-foursignal triplets as illustrated in FIG. 2. Because many of the signaltriplets are grouped together as separate digital resources, there are afewer number of cross-bar register outputs to provide correspondingdigital levels to select the groups of signal triplets. FIG. 3 shows, insimplified form, only three signal triplets. These signal triplets arenot in the same group, and thus a separate XBR output selects theindividual signal triplets. However, those skilled in the art canreadily expand and replicate the cross-bar decoder cells to accommodateas many signal triplets as desired. When an output of the cross-barregister 50 is driven high, the respective signal triplet is selectedand activated.

Each cross-bar decoder cell in the first column, such as column cells72, 74 and 76, can be connected to a Data₀-in signal line 102. In thesecond column of the cell matrix, cells 78 and 80 can be connected tothe Data₁-in signal line 104. The last matrix column has only a singlecell 82, and thus can be connected to a Data₂-in signal line 106. Thesedata-in lines are effective to route data from the respective I/O pinreceivers through the priority cross-bar decoder cells, to the dataresources 12. The data-in signals follow a path through the prioritycross-bar decoder 10 based on the priority encoded therein.

Each matrix cell of the priority cross-bar decoder 70 situated in thefirst column, namely cells 72, 74 and 76, is provided an Enable₀-outsignal 108 and a Data₀-out signal 110. Each such column cell provides arespective enable output line 112, 114 and 116, all of which areconnected to the inputs of an OR gate 118 to provide the Enable₀-outsignal 108. The column cells 72, 74 and 76 also provide respective dataoutputs 118, 120 and 122 which are connected to a second output OR gate124 for providing the Data₀-out signal 110. Based on the priorityencoded within the column of cells, only one cell in a column is enabledto both receive and transmit data with respect to the I/O pin associatedtherewith. Hence, only one input to both OR gates 118 and 124 will beactive at one time. The other control line connected to the enable ORgates 118, 130 and 143 will be discussed below.

The cells 78 and 80 in the second column of the priority cross-bardecoder 70 also provide respective enable outputs on lines 126 and 128.These two lines 126 and 128 are coupled to an output OR gate 130 toprovide an Enable₁-out signal 132. In like manner, data outputs 134 and136 are coupled from cells 78 and 80 to a second output OR gate 138 toprovide the Data₁-out signal 140. The last column cell 82 provides anEnable₂-out signal 142 and a Data₂-out signal 144. Since there is only asingle cell 82 in the last column of the exemplary matrix, no dataoutput OR gate is required.

As noted above, each column cell receives data from the respective I/Opin driver by way of the data-in lines 102, 104 and 106. Each data-inline, for example line 102 associated with the first column of cells, isconnected to an AND gate. Data₀-in line 102 is connected to AND gate 146in cell 72, gate 148 in cell 74 and gate 150 in cell 76. The output offirst AND gate 146 in cell 72 is coupled to the Sig₀-in line 90. Theoutput of the second AND gate 148 is coupled to an input of an OR gate152 and produces the Sig₁-in signal on line 154. The output of the thirdAND gate 150 is connected to an input of an OR gate 156 to produce acorresponding signal on the Sig₂-in line 158. The Data₁-in line 104 ofthe second column of cells 78 and 80 is coupled to AND gate 160 in cell78. The output of AND gate 160 is coupled to the other input of OR gate152. Based on which cell 74 or 78 in the row is made active, the OR gate152 will provide the selected Data-in signal and route the same to theSig₁-in line 154.

As noted above, the Data₀-in signal on line 102 is coupled to the ANDgate 150 of cell 76. In cell 80, the Data₁-in signal on line 104 iscoupled to AND gate 162. The output of AND gate 162 is coupled toanother input of the OR gate 156. The Data₂-in signal on line 106 iscoupled to an AND gate 164 in cell 82. The AND gate 164 has an outputcoupled to yet another input of the OR gate 156. The selected signal onthe OR gate 156 is coupled to the Sig₂-in line 158.

The input and output functions of the cross-bar decoder 70 operate inthe following manner. For purposes of example, it is assumed that allthree cross-bar register signals on lines 96, 98 and 100 are driven toan active high state. This means that these signals on the triplet lines84, 86 and 88 are selected and will be active, and will be routed in apriority manner to the three output pins shown in FIG. 5. For example,it is further assumed that the I/O pins 170, 172 and 174 are configuredto function as output pins. To that end, elementary logic circuitsassociated with the digital resources 12 will drive the enable lines(Enable₀-out, Enable₁-out and Enable₂-out) to a logic low level. A logiclow state thus drives the enable output line 94, the enable output line176 and the enable output line 178 to a logic low. In certaincircumstances, when the I/O pins 170-174 are configured as output pins,the input signal lines Sig_(x)-in lines 90, 154 and 158 couple thesignals output from the I/O pins, back to receive circuits in thedigital resources 12 to compare the same. The transmitted signal can becompared with the signal returned to determine if bus contention isinvolved. The data from the digital resources 12 is coupled on theSig_(x)-out lines 92, 180 and 182 to the respective rows of cells in thepriority cross-bar decoder 70.

The priority encoding scheme operates in the following manner. Thehighest priority signals are coupled in the triplet 84 to the top row ofcells of the cross-bar decoder 70. This corresponds to cross-bar cell72. The next highest priority triplet 86 of signals is coupled to themiddle row of the cross-bar decoder 70. This corresponds to cells 74 and78. The lowest priority of signals is coupled in triplet 88 to thebottom row of cross-bar decoder cells. This corresponds to cells 76, 80and 82. As noted above, the highest priority signal is coupled to Pin0,the next priority signal is coupled to the next pin which, in theexample, is Pin1. The lowest priority of the three signals is coupled tothe third pin, Pin2. The connection is carried out in the followingmanner, again assuming that all three signal triplets 84, 86 and 88 areactive.

When the cross-bar register signal XBR₀ drives line 96 to a logic high,such level selects transmission AND gates 184 and 186 in cell 72. TheXBR₀ signal is also coupled to the inverting input of priority AND gate188 located within cell 74. The output 190 of AND gate 188 is therebydriven to a logic low. The logic high signal of the XBR₀ signal and thelogic low output 190 of the priority AND gate 188 are coupled to an ORgate 192 in cell 74. With these logic levels, the output 194 of the ORgate 192 is driven to a logic high. The logic high on line 194 iscoupled to an inverting input of priority AND gate 196 of cell 76. Theoutput of the AND gate 196 drives line 198 to a logic low. It can beseen that the transmission AND gates 200 and 202 in cell 74 control thecoupling therethrough of Sig₁-out signal on line 180 and the Enable₁-outsignal on line 176. With the signal on conductor 190 being driven to alogic low by priority AND gate 188, this disables the signals of thesecond triplet 86 from being passed through the transmission gates 200and 202 to the respective output OR gates 118 and 124. In like manner,the output of priority AND gate 196 of cell 76 disables transmission ANDgates 204 and 206. This prevents passage therethrough of the Sig₂-outsignal on conductor 182, and the Enable₂-out signal on conductor 178.These two signals cannot thereby be coupled to the output OR gates 118and 124. As such, the only signal that is passed to the output OR gates118 and 124 is the highest priority signal, namely, Sig₀-out andEnable₀-out. These output OR gates couple the respective signals to thefirst I/O pin 170, via the driver circuit 212. The operation of thedriver circuit 212 will be described in more detail below.

The data resource signals carried in the second triplet 86 on lines 180and 176 are not only coupled to the first cell 74 in the second row, butalso to the second cell 78 in such row. As such, the digital signalscarried on lines 180 and 176 are coupled to transmission AND gates 208and 210 in cell 78. The priority AND gate 214 in cell 78 determineswhether the Sig₁-out and Enable₁-out signals will be transferred throughthe transmission AND gates 208 and 210 to the respective output OR gates130 and 138. It is noted that in the example, XBR₁ drives line 98 to alogic high to thereby select the signals of the second triplet 86. Thelogic high on line 98 is also carried to the second cell 78 in the row,and particularly to priority AND gate 214. The logic low driven bypriority AND gate 188 in cell 74, is coupled to the inverting input ofpriority AND gate 214 of cell 78. The output of priority AND gate 214 isthus a logic high. This enables transmission AND gates 208 and 210 toroute therethrough the two signals on lines 180 and 176 of triplet 86.The outputs of transmission AND gates 208 and 210 are coupled onrespective lines 134 and 126 to the output OR gates 130 and 138. Theselogic signals are also coupled to Pin1, designated by reference numeral172, via the driver circuit 216.

It is noted that the two signals on lines 182 and 178 of the thirdtriplet 88 are not coupled through the respective transmission AND gates218 and 220 of the third row cell 80. The reason for this is that thelogic high output produced by priority AND gate 214 in cell 78 iscoupled to the inverting input of priority AND gate 222 of cell 80. Theoutput of priority AND gate 222 thus drives a logic low to therespective inputs of transmission AND gates 218 and 220. Thus, the twosignals of triplet 88 on lines 182 and 178 are not passed via the outputOR gates 130 and 138 to Pin1.

From the foregoing operation of the priority cross-bar decoder 70described thus far, it can be seen that a cell, such as cell 72, rankedwith the highest priority, disables all other cells therebelow in thecolumn, namely cells 74 and 76. The signals assigned the next priority,such as those of triplet 86, pass to the next column of cells, namelycell 78, since the first cell 74 of that row was disabled. Cell 78 isconfigured to route the digital signals to the second output pin, andalso to disable the cell therebelow in the column, namely cell 80. Thus,cells 72 and 78 are enabled to pass the signals to the respective I/Opins 1 and 2, but cells 74, 76 and 80 are disabled.

With regard to the third triplet 88 of signals, such signals are carriedon lines 182 and 178 through the first two cells (76 and 78) in thebottom row, to cell 82. These two signals are coupled respectively totransmission AND gates 224 and 226. It is noted from the example thatthe third triplet 88 of signals are selected and made active by reasonof the cross-bar signal XBR₂ being driven high. This logic high iscarried on line 100 through cells 76 and 78 to a priority AND gate 228of cell 82. Whether the two signals of triplet 88 are carried throughthe transmission AND gates 224 and 226 is determined by the output 230of priority AND gate 228. As noted above, the non-inverting input ofpriority AND gate 228 is a logic high, as driven by the XBR₂ signal. Theoutput of priority AND gate 222 (cell 80) on line 232 is coupled to oneinput of OR gate 234. The other input of OR gate 234 is driven by theoutput 198 of the priority AND gate 196 of cell 76. The input 198 ofpriority AND gate 222 of disabled cell 80 is a logic low. With bothinputs of OR gate 234 being driven to logic low states, the outputthereof is also a logic low. The output of OR gate 234 is coupled to aninverting input of priority AND gate 228 of cell 82. With a logic highon the non-inverting input, and a logic low on the inverting input ofpriority AND gate 228, the output 230 thereof is driven to a logic high.The logic high on output 230 enables transmission AND gates 224 and 226in cell 82. Hence, the two signals on input lines 182 and 178 passthrough the transmission AND gates 224 and 226 of cell 82 to the I/Opin, namely Pin2. Again, these two signals are coupled via the drivercircuit 236 to the third pin (Pin2). From the foregoing, the prioritycross-bar decoder 70 automatically couples input signals in a prioritymanner to the first pin, second pin and third pin of the integratedcircuit.

If, for example, the signals of the second triplet 86 are not madeactive, then the priority cross-bar decoder 70 automatically takes thisinto consideration and shifts the third triplet 88 signals to the secondI/O pin (Pin1), rather than the third I/O pin. The signals of the secondtriplet 86 are made inactive by driving output XBR₁ of the XBR registers50 to a logic low state. Hence, a logic low will exist on line 98, whichline is coupled to the priority AND gate of cell 74, as well as priorityAND gate 214 of cell 78. For the same reasons described above, signalsof the first triplet 84 will be routed through the transmission ANDgates 184 and 186 of cell 72 through intermediate circuitry to the firstI/O pin (Pin0). Again, circuitry of cell 72, which is the highestpriority cell, disables the transmission AND gates of the cellstherebelow, namely cells 74 and 76. With the cross-bar register outputXBR₁ output 98 driven to a logic low, the input of priority AND gate 214of cell 78 is also driven to a logic low. The output of the priority ANDgate 214 is thus at a logic low level. This logic low level disablestransmission AND gates 208 and 210 of cell 78, thereby preventingpassage therethrough of the two signals of the second triplet 86. Hence,cells 74 and 78 in the second row are both disabled. Signals of thesecond triplet 86 are thus not routed through the priority cross-bardecoder 70.

With reference to cell 76, it is noted that such cell is disabled by theaction of the top priority cell 72. As such, the output of the priorityAND gate 196 is a logic low. This logic low is coupled to an invertinginput of priority AND gate 222 of cell 80. The other inverting input ofpriority AND gate 222 is also at a logic low, because this logic levelis produced by the output of priority AND gate 214 of cell 78. Thenon-inverting input of priority AND gate 222 of cell 80 is at a logichigh, as this is the logic level of the XBR₂ signal. As such, the outputof priority AND gate 222 is at a logic high state, thereby enabling thetransmission AND gates 218 and 220. When enabled, the transmission ANDgates 218 and 220 pass the two signals of the triplet 88 to the outputOR gates 130 and 138. These two signals of the third triplet 88 are thusrouted to the second I/O pin, namely Pin1. When the second triplet 86signals are made inactive, the third triplet 88 signals are thus shiftedfrom the third I/O pin to the next higher priority pin, namely Pin2.

With reference to OR gate 234 of cell 80, it is noted that one input isa logic high and the other input is a logic low. As such, the outputthereof is a logic high, which logic state is coupled to the invertinginput of priority AND gate 228 of cell 82. The output of priority ANDgate 228 is thus a logic low, thereby disabling transmission AND gates224 and 226 of such cell. Hence, neither the Sig₂-out or the Enable₂-outsignals carried on lines 182 and 178 are passed to the driver circuit236 of the third pin (Pin2).

Without encumbering this description with the details, those skilled inthe art can readily verify that if the first triplet 84 of signals aremade inactive, the second triplet 86 signals are shifted to first pin(Pin0) and the third triplet 88 signals are shifted to the second pin(Pin 1). If, on the other hand, the first triplet 84 and the secondtriplet 86 signals are made inactive, the cells 72, 74, 78, 80 and 82are disabled. With this arrangement, the signals of the third triplet 88are routed via cell 76 to the first I/O pin (Pin0). It can thus be seenthat the highest priority signals are coupled to the highest prioritypins, and if any signal is absent, lower order priority signals areshifted to use the I/O pins having the next highest priority. Lowerpriority pins may thus be unused when some of the signals are inactive.

The foregoing describes the operation of the priority cross-bar decoder70 when the I/O pins are configured as output pins. When theEnable_(x)-out signals of the three triplets are driven to a logic highlevel, the respective driver circuits 212, 216 and 236 configure the I/Opins as inputs to receive data from external devices. In the preferredform, some I/O pins can be configured as inputs, while at the same timeother I/O pins can be configured as outputs. This is achieved by drivingthe various Enable_(x)-out signals to corresponding states.

It is further noted that other types of logic circuits can be employedto carry out the foregoing priority routing of signals. Instead ofemploying AND gates 146 and 184, conventional bidirectional transmissiongates can be used. In this event, the output OR gates 124 can beeliminated.

Reference is now made to FIG. 5 where there is shown in detail one pindriver circuit 212. The other driver circuits 216 and 236 areconstructed and operate in an identical manner. The triplet signals onlines 102, 108 and 110 associated with the first column of thecross-point decoder 70, are coupled to the driver circuit 212 of thefirst pin, Pin0. The second triplet of signals on lines 104, 132 and 140associated with the second column of the cross-bar decoder 70 arecoupled to the second pin driver 216. Lastly, the third triplet ofsignals carried on lines 106, 145 and 144 are coupled to the thirddriver 236 associated with the third I/O pin.

When the XBARE signal of FIG. 3 is driven to a logic low, the output ofenable OR gates 118, 130 and 143 are driven to logic high states. InFIG. 5, the logic high state is coupled through an inverter 240 topresent a logic low on an input of NAND gate 242. The output of the NANDgate 242 drives a P-channel driver transistor 244 of a push-pull driver,thereby turning it off. The output 108 of the enable OR gate 118 alsodrives an input of a NOR gate 246 in the pin driver circuit 212. Theoutput of the NOR gate 246 drives an N-channel driver transistor 248 ofthe push-pull driver to a low level, thereby turning it off. As aresult, push-pull output 250 of the driver transistors 244 and 248 is ina high impedance state, which state is coupled to the corresponding I/Opin 170. Thus, when the XBARE signal is at a logic low state, all of theI/O pins are driven to a high impedance state. This feature can beadvantageously used when XBRx select signals applied to the prioritycross-bar decoder 70 are “settling out” to a stable state. This preventstemporary-state and glitches from appearing at the I/O pins. However,when the XBARE signal is low during this transition period, no erroneoussignals will appear at the I/O pins. Those skilled in the art may alsoutilize additional circuits connected to the P-channel driver transistor244 and the N-channel driver transistor 248 to prevent both suchtransistors from being driven into conduction at the same time.Moreover, those skilled in the art may find that not all drivers shouldbe driven into a high impedance state at the same time. Rather, bycoupling the XBARE signal to different ones of the OR gates 118, 130 and143, some drivers may be operational, and others may be configured to ahigh impedance state.

With reference again to the I/O driver 212, it is noted that if thedriver is configured to an operational state, in which logic level online 1

a low level, output pin 170 can be given to the logic levelcorresponding to the data on the line 110. As noted in FIG. 5, Data₀-outsignal on line 110 is coupled to an input of NOR gate 246, as well as toan input of the NAND gate 242. For purposes of example, it is assumedthat the driver transistors 244 and 248 are to be operated in apush-pull manner. Accordingly, the push-pull control line 252 is drivento a logic high level. Assuming further that the logic level on theData₀-out 110 is a logic high, then the output of the NOR gate 246 willbe logic low, thereby turning off the N-channel driver transistor 248.On the other hand, the output of the NAND gate 242 will be at a logiclow level, thereby turning the P-channel driver transistor 244 on. TheI/O pin 170 will thus be driven to a logic high state, corresponding tothe logic state on the Data₀-out line 110.

If, on the other hand, the logic state on the Data₀-out line 110 is at alogic low level, then the output of the NOR gate 246 will be logic highlevel. The output of the NAND gate 242 will be at a logic high levelalso. The P-channel driver transistor 244 will thus be turned off, whilethe N-channel driver transistor 248 will be driven into conduction. Thelogic state that the I/O pin will thus be at a logic low level,corresponding to the logic state on the data line 110.

In the event that the I/O pin 170 is to be provided with a weak pull-up,then the line 254 is driven to a logic low state. If the output of theNOR gate 246 is also at a logic low level, the OR gate 256 will drivethe P-channel driver transistor 258 into conduction. The pull-uptransistor 258 is constructed with a long channel, thereby providing ahigh resistance between the supply voltage VDD and the I/O pin 170. Aweak pull-up to the I/O pin 170 is thus provided. The weak pull-upcontrol lines 252 and 254 are coupled to all the driver circuits, andare controlled by way of the XBR registers 50. Each driver circuit 212,216 and 236 is controlled with a push-pull control signal line, oneshown as reference number 252. These push-pull control lines arecontrolled by the PRT registers 54. In order to configure the I/O pin170 for input of digital signals, the Enable₀-out signal on line 108 isdriven to a logic high state. As noted above, both transistors 244 and248 are turned off, thereby placing the I/O pin 170 in a high impedancestate. Accordingly, external signals can be applied to the I/O pin 170.The input signals are coupled through a receiver 260, and therethroughto the Data₀-in line 102. With reference to FIG. 3, the input datasignals on line 102 are coupled to the AND gates 150, 148 and 146 of therespective cross-bar decoder cells 76, 74 and 72. In the first exampledescribed above, all three triplet signals 84, 86 and 88 are active.Since the triplet 84 is of the highest priority, the other cells in thecolumn under cell 72 are disabled by virtue of the outputs of thepriority AND gates 188 and 196 being at a logic low level. At thesecorresponding logic low levels, the inputs of AND gates 148 and 150 arealso at a logic low, thereby disabling transfer therethrough of theincoming data signal on line 102. However, the control input of AND gate146 is at logic high, thereby allowing the signal on line 102 to passtherethrough and be routed to the Sig₀-in line 90. Data can thus becoupled on line 90 to the corresponding digital resource. As can beappreciated, the same priority applies to signals received by thecross-bar decoder 70 from the I/O pins, as with signals transferred fromthe cross-bar decoder 70 to the corresponding I/O pins.

In like manner, the input signal coupled from I/O pin 172 pass throughthe AND gate 160 of cell 78 to the line 154 of triplet 86. The AND gate162 of cell 80 is disabled, by virtue of the output 232 of the priorityAND gate 222 being driven to a logic low level. Lastly, any digitalsignal input via I/O pin 174 is coupled through the AND gate 164 of cell82, and thus passes to the gate OR 156 and is coupled to the Sig₂-inline 158. A similar analysis can be carried out to verify that,depending upon which cells are enabled or disabled, data signals on theData₀-in line 102 can be transferred via respective AND gates 148 or 150to the Sig_(x)-in line of either the second triplet 86 or the thirdtriplet 88. The Data₁-in signals on line 104 can also be coupled via ANDgate 162 to the third triplet 88.

As noted in FIG. 2, not all cell locations of the priority cross-bardecoder 10 need be populated with a cross-bar cell. Rather, some spaces56 are vacant. This means that the corresponding digital resource signalCEX0 cannot be coupled to P0.7. FIGS. 6 and 7 depict a prioritycross-bar decoder 270 similar to that shown in FIG. 3, but where celllocation 80 is vacant. As a result, the signal lines extending laterallyfrom cell 76 are coupled directly to the corresponding inputs of cell82. As a result of this vacant cell location, the signals from the thirdtriplet 88 cannot be coupled to the second I/O pin, Pin1. The operationof the priority cross-bar decoder 270 is otherwise the same as thatdescribed above in connection with FIG. 3.

FIG. 8 illustrates a 5×4 matrix of priority cross-bar decoder cells.Many of the fourteen cells are similar to those shown above inconnection with FIG. 3. For example, cell 0,0 of matrix 280 is identicalto cell 72 of FIG. 3. Cells 0,1 and 1,1 of matrix 280 are similar torespective cells 74 and 78 of matrix 70. Cells 0,2 and 0,3 are similarto cell 74 and, cell 3,3 is similar to cell 78. Cell 0,4 is similar tocell 76, and cells 1,4 and 2,4 are similar to cell 80. Lastly cell 3,4is similar to cell 82. Cells 1,2 and 1,3 and 2,3 of the matrix 280 arebounded by other neighbor cells, and are shown in enlarged form. Thematrix of priority cross-bar decoder cells are otherwise operated in thesame manner described above in connection with FIG. 3.

The priority cross-bar decoder 280 of FIG. 8 includes yet other featureswhich could be incorporated in the embodiment shown in FIG. 3. Forexample, the priority cross-bar decoder 280 could include defaultcircuits 282, one of which is shown in enlarged form as referencenumeral 284. The default circuits 282 route the signals of themicroprocessor port latches 16 to control the driver circuits in theevent that no other cross-bar signal is assigned to the driver circuit.This allows all unassigned I/O pins to serve as general purpose digitalI/O. This aspect of the invention is shown in FIG. 1, where themicroprocessor port latches 16 are coupled to the priority cross-bardecoder 10 by way of eight-bit lines 34, 35 and 36. With reference againto FIG. 8, the default circuits 282 include four identical circuits,each coupled to a respective data bit DO₀-DO₃. These four data bits arecoupled from four outputs of a port data latch 16 (FIG. 1). It should benoted that the drivers shown in FIG. 8 are identical to those notedabove in connection with FIG. 5. An alternative embodiment could utilizean additional level of multiplexing between the cross-barData_(x)-outputs and the pin driver circuits. These multiplexers couldbe controlled by the microprocessor to override the cross-bar outputsand thereby directly control the driver circuits with the port latchregisters.

An enlargement of one override circuit is shown as reference numeral284. Here, the DO₀ data bit is applied from the microprocessor portlatch 16 to one input of AND gate 286. Enable control line 288 iscoupled to an inverting input of AND gate 286, as well as to an enableoutput directed to the enable OR gate 302. The enable control line 288is coupled from the cell (0,4) located thereabove. In the example, cell(0,4) is similar to cell 76 shown in FIG. 3. The enable control line 288would be an extension of conductor 194 which constitutes the output ofthe OR gate 192 in cell 74 of such figure. In any event, when one ormore of the cross-bar register outputs (XBR_(x)) is driven to a logiclow, enable control line 288 is also driven low. As a result, any dataapplied to the DO₀ input 292 of the override circuit 284 is coupled tothe AND gate output 294. The output of the AND gate 294 is coupledthrough the output OR gate 296 to the driver 298. Hence, any digitalsignal applied to the data input 292 of the AND gate 286 is coupled bythe driver 298 to the output Pin 0.0.

It is noted that the priority of the digital resource signals isassigned by connecting the highest priority signal as the first signaltriplet 84 to the cross-bar decoder 70. The next highest priority signaltriplet 86 is then connected as the second signal triplet to thecross-bar decoder 70, and so on. There may be applications where thepriority of the signals from the digital resources should be changedduring processing. In this event, shifting or rearranging circuits atthe signal input of the cross-bar decoder 70 can be utilized to shift orotherwise substitute or rearrange the input signals to different inputsof the cross-bar decoder 70. With such a signal rearranging circuit, thepriority of the signals can be changed during processing.

FIG. 9 is a diagram of a general cross-bar decoder 310 for theassignment of digital resource signals to I/O pins in a microcontrollerapplication. The signals to be assigned connect along the rows of thearray 310. The I/O pins to be assigned connect down the columns. Eachcell shown connects a triplet of signals to its associated I/O pin,depending on the logic state of its En_(ij) enable input. In general,the enable controls for each cell of a row will be generated by adecoder 312 associated with the row. The input to each decoder 312 iswritten with logic states by microcontroller software which establishesthe desired signal-to-pin assignment. In the example of the decoder 310illustrated, there are four cells in a row, and thus the decoder 312would be written with four logic states corresponding to which cells ofthe row will be enabled and which cells will not be enabled to route thetriplet signals. The specific details of the decoders 312 are strictly afunction of the type of signals to be assigned. Typically, the decoder312 would be designed such that at most only one of its En_(ij) outputscan be asserted active at a given time. However, in some cases, it maybe desirable to assign a signal triplet to multiple I/O pinssimultaneously. Also, although the general case shows each signaltriplet having its own decoder 312, signals which must be assigned ingroups could share a single decoder 312. In such circumstances, certaincells in the array 310 will in fact never be activated and hence couldbe removed from the array without altering the operation of thecross-bar decoder 310. As in the priority cross-bar decoders describedabove, the AND gates in the cells can be replaced with bidirectionaltransmission gates (and the OR gates which generate the pin Out and OEsignals can be removed).

Each array cell can be constructed identically. One cell 314 is shown indetail in the enlargement. The data input from the digital resource isidentified as O_(i). The enable input to the cell 314 is OE_(i). Thedata and enable inputs from the digital resource are daisy-chained toeach cell in a row. The output of the decoder 312 is input to the cellas signal En_(ij). The En_(ij) signal, when at a logic high state,enables the AND gates 316 and 318 to route the respective input signalsto corresponding output OR gates, two of which are shown as referencecharacters 322. The En_(ij) signal also enables AND gate 320 to routesignals from the respective I/O pin through the cell 314 to the digitalresource circuits. A bidirectional transfer of signals can thus beaccomplished with each cell of the cross-bar decoder 310.

An AND gate 324 receives the outputs of both the OR gates 322 of thecolumn for coupling such signals to the I/O pin driver circuit 212. Asignal on control line 326 can disable the AND gate 324 to inhibit thecolumn signals from being transferred to the pin driver 212. The variousother features of the priority cross-bar decoders described above can beutilized in conjunction with the decoder 310.

When the cross-bar decoder 310 is integrated with a digital controller,a great degree of flexibility is achieved in assigning the digitalresource signals to the different I/O pins.

Although the preferred embodiment has been described in detail, itshould be understood that various changes, substitutions and alterationscan be made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A circuit for assigning digital resources to pins of an integratedcircuit, comprising: a plurality of pins of said integrated circuit; amicroprocessor formed in said integrated circuit; a plurality of digitalresources formed in said integrated circuit; a cross-bar matrix having aplurality of signal inputs coupled respectively to said digitalresources, and a plurality of signal outputs coupled to said integratedcircuit pins, said cross-bar matrix controlled by said microprocessorfor coupling said ones of said signals inputs to different said signaloutputs, whereby said digital resources can be coupled to different pinsunder control of said microprocessor.
 2. The circuit of claim 1, whereinsaid cross-bar matrix includes a plurality of cells, each said cellbeing identically constructed.
 3. The circuit of claim 1, wherein saidcross-bar matrix is constructed as a plurality of rows associated withsaid signal inputs, and a plurality of columns associated with saidsignal outputs, and each cell of a row is controlled by saidmicroprocessor for coupling or not coupling digital resources at arespective signal input to a signal output.
 4. The circuit of claim 3,wherein each said cell is individually controlled by saidmicroprocessor.
 5. The circuit of claim 3, wherein each row of saidcross bar matrix includes a register with a plurality of outputs, eachsaid output controlling operation of a respective cell in a row.
 6. Thecircuit of claim 1, wherein each said row is associated with a signaloutput and each said column is associated with a signal input, wherebysaid cross-bar matrix is adapted for coupling signals therethrough in abidirectional manner.
 7. The circuit of claim 6, wherein said processoris programmed to control whether said pins are configured as input pinsor as output pins.
 8. The circuit of claim 7, further including acontrol signal generated by said microprocessor and coupled through saidcross-bar matrix for controlling whether a pin is to be configured as aninput pin or as an output pin.
 9. The circuit of claim 8, furtherincluding a pin driver circuit for providing input/output circuits withregard to each said pin.
 10. A cross-bar matrix, comprising: a pluralityof matrix cells arranged in rows and columns, each said row of cellsassociated with a common signal input, and each column of cellsassociated with a common signal output; and each said cell having acontrol input for controlling whether the cell is to couple a signal onthe associated common signal input to a signal output associated withthe cell, whereby any signal of a row can be coupled to any signaloutput.
 11. The cross-bar matrix of claim 10, wherein each said cell ofa row is coupled to a data signal line for receiving the same datasignal, and each cell in a row is coupled to a different control linefor controlling whether the cells in the row are to couple the datasignal to a respective signal output.
 12. The cross-bar matrix of claim11, wherein said control lines are coupled to a circuit that enablesonly one control line in a row at a time.
 13. The cross-bar matrix ofclaim 11, wherein each cell of a row is coupled to an output enablesignal line for receiving an output enable signal from the digitalresources, and said control line controls whether the cells in the roware to couple the output enable signal to a respective signal output.14. The cross-bar matrix of claim 11, wherein each said cell of a columnhas a data signal output coupled to a logic circuit for providing asingle output corresponding to a selected cell of the column.
 15. Thecross-bar matrix of claim 14, further including an enable circuitcoupled between said logic circuit and a pin associated with therespective column, said enable circuit being controlled to enable ordisable said data signals from being coupled to said respective pin. 16.The cross-bar matrix of claim 11, wherein each cell in a row includes acircuit for receiving a data signal from a pin associated with therespective column, and said control line controls whether said datareceiving circuit is to couple received data from said matrix to thedata resource.
 17. The cross-bar matrix of claim 16, wherein each cellof a row includes a data receive output line coupled to a logic circuit,said logic circuit providing an output to the data resource of the cellin the row that was enabled by said control line.
 18. A cross-barmatrix, comprising: a plurality of cells arranged in rows and columns,each cell in a row associated with a common data signal, and each cellin a row associated with a common output enable signal, and each cell ina column being associated with a common I/O pin; each cell in a rowreceiving a different enable signal for enabling the respective cell tocouple the data signal and the output enable signal to a respective I/Opin, each cell in a row including a data signal circuit responsive tothe enable signal for coupling therethrough the data signal, and eachcell in a row including an output enable signal circuit responsive tothe enable signal for coupling therethrough the output enable signal;each cell in a row including a data receive circuit for receiving a datasignal from the respective I/O pin, and responsive to said enable signalfor coupling the data receive signal from the I/O pin to the dataresource.
 19. The cross-bar matrix of claim 18, wherein each cell ofsaid matrix is identically constructed.